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Re: [Xen-devel] [PATCH] xen-blkback: defer freeing blkif to avoid blocking xenwatch

On Mon, May 12, 2014 at 6:40 PM, Boris Ostrovsky
<boris.ostrovsky@xxxxxxxxxx> wrote:
> On 05/09/2014 07:34 PM, Valentin Priescu wrote:
>> From: Valentin Priescu <priescuv@xxxxxxxxxx>
>> Currently xenwatch blocks in VBD disconnect, waiting for all pending I/O
>> requests to finish. If the VBD is attached to a hot-swappable disk, then
>> xenwatch can hang for a long period of time, stalling other watches.
> Note that we have a GSoC student (copied here) who is going to be looking at
> xenwatch's single-threadness (?) over the summer.

AFAIK, in older kernel versions, you could pass a flag to a registered
watch that told
xenwatch to spawn a new kthread when it handles the events. That
didn't work well
and it was removed.

Anyway, whatever solution he comes up with, I think he still needs to
make similar
changes in the disconnect path for blkback. Besides, blocking
uninterruptible for a long
period of time is not OK.


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